The present invention relates to an electrophotographic copying machine and, more particularly, to a device for limiting the amount of light passing to a copy document of the copying machine.
An electrophotographic copying machine produces an electrostatic latent image on an optical-sensitive member with an optical system. The latent image corresponds to an image on a copy document such as a manuscript or book to be copied. Toner particles are electrically adhered to the latent image, so that the latent image becomes visible to form a toner image. The toner image is transferred onto a copy paper via a transference charger.
conventionally, the optical system for directing a light image of the copy document onto the optical-sensitive member is constructed so that the copy document is exposed to light emitted by a light source and its reflected light is focused onto the optical-sensitive member by some lens. Part of the optical system for focusing the reflected light from the copy document onto the optical-sensitive member includes a device for limiting light passing to a copy document which is positioned between the copy document and the optical-sensitive member.
In controlling the light amount, the position of the device is altered. However, the conventional device cannot control the light amount precisely and uniformly over the surface of the optical-sensitive member. Further, the conventional device is rather long, so that the distance between the copy document and the optical-sensitive member becomes rather long, so that the copying machine is prevented from being compact. Accordingly, it is desired to provide an improved device.